Shredding machine with expansion chamber



Sept. 13, 1955 w. R. WEIGHAM ETAL SHREDDING MACHINE WITH EXPANSION CHAMBER 2 Sheets-Sheet 1 Filed May 29, 1953 F Jr 2F 4, z /M y o w 9 7 m. o m. E b D P 7 7 Sept. 13, 1955 Filed May 29, 1953 W. R. WEIGHAM ET L SHREDDING MACHINE WITH EXPANSION CHAMBER FiC5.4. 2

2 Sheets-Sheet 2 United States Patent SHREDDING MACHINE WITH EXPANSION CHAMBER William Reginald Weigham, John O. Smith, and George M. Johnson, Coventry, England, assignors to Courtaulds Limited, London, England, a British company Application May 29, 1953, Serial No. 358,284

2 Claims. (Cl. 241255) This invention relates to shredding machines for alkali cellulose.

In one method of manufacturing viscose, sheets of wood pulp are steeped in caustic soda solution to convert the cellulose sheets to alkali cellulose sheets which are pressed to remove excess liquid and then shredded to form particles known as crumbs. The crumbs are aged under uniform conditions for a predetermined period, converted to cellulose xanthate by reaction with carbon disulphide, and the cellulose xanthate is dissolved in caustic soda solution to form viscose.

A common form of shredder is a Pfleiderer. A suggested alternative is described and illustrated on pages 173 and 174 of the Final Report No. 290, Item No. 22, 31 of the British Intelligence Objectives Sub-Committee, according to which operation alkali cellulose sheets are fed through a chaff cutter and then through a horizontal, cylindrical shredding drum in which a screw turning at 230 revolutions per minute, breaks up the sheets and ejects the crumbs so formed through an opening in the end wall of the drum; the screw carries four parallel bars on its periphery and teeth on the bars pass close to fixed teeth on the inner wall of the drum.

The object of the present invention is to subject all the alkali cellulose to substantially uniform conditions as it is fed through and out of a drum shredder.

According to the present invention, a drum shredder for alkali cellulose comprises a drum having a shredding surface on its internal wall, a rotor mounted centrally within the drum having one or more co-operating shredding surfaces on its periphery and being capable of conveying the alkali cellulose axially towards an outlet and driving means for rotating the rotor so that the alkali cellulose is thrown into an annular shredding region defined between the shredding surface of the drum and the co-operating shredding surfaces of the rotor wherein the rotor extends beyond the annular shredding region at the outlet end of the drum and the annular shredding region merges into a space not swept by the rotor so that the shredded alkali cellulose is freed from mechanical pressure and hence can expand prior to its discharge through the outlet.

In one embodiment of the invention, the annular shredding region merges into a collecting chamber c0- axial with and having a diameter greater than that of the drumand the rotor protrudes into the collecting chamber directly above the outlet at the bottom of the collecting chamber. The collecting chamber may be of uniform cross section or it may have a cross section increasing from the point at which it joins the drum. The collecting chamber may be provided with a chute through which the shredded alkali cellulose may fall under the action of gravity. Preferably, the rotor comprises a screw conveyor divided longitudinally by a bafile of width equal to the effective diameter of the screw conveyor and the co-operating shredding surfaces comprise at least one bar, parallel to the axis of the "ice screw conveyor, having a series of teeth along its length and mounted in slots cut into the peripheral edges of the screw conveyor so that the teeth are in line with but do not extend beyond the periphery of the screw conveyor. The screw conveyor is rotated at such a speed that the alkali cellulose is thrown outwardly into the annular shredding region and is also conveyed towards the outlet. The baffle prevents alkali cellulose passing through the drum without passing through the annular shredding region. The screw conveyor may extend through the collecting chamber to the end wall of the collecting chamber or may stop short of the end wall.

In a further embodiment of the invention, the drum shredder comprises a screw conveyor and a drum having a shredding surface on the inner wall, an end wall and an outlet in the floor of the drum. The outlet is defined on one side by the end wall and the screw conveyor extends part way over the outlet but stops short of the end wall. A chute is mounted directly below the outlet so that shredded alkali cellulose may fall under the action of gravity.

Specific examples of drum shredders constructed in accordance with the present invention are illustrated by the accompanying drawing, in which:

Figure 1 is a front view partly in section of one drum shredder,

Figure 2 is a section through the line 2-2 of Figure 1,

Figure 3 is an enlargement of part of Figure 2,

Figure 4 is a fragmentary front view partly in section showing a shredder with an alternative form of collecting chamber,

Figure 5 is a fragmentary front view partly in section of a further form of shredder, and

Figure 6 is a section through the line 6--6 of Figure 5.

The apparatus shown in Figure 1 comprises a feeding chamber 1, a horizontal drum 2 and a collecting chamber 3 having a greater internal cross section than the drum 2. A shaft 4 mounted in bearings 5, 6 and passing centrally through the chamber 1, the drum 2 and the chamber 3, is rotated by a pulley 8 and a belt 7. A screw conveyor 9 is mounted on the shaft 4 and extends from the feeding chamber 1 through the drum 2 and part way into the collecting chamber 3. The inner wall 10 of the drum 2 is grooved to form pyramidal teeth 11 (only partly shown in Figure l) and the periphery of the screw conveyor 9 just clears the teeth V 11, for example by about of an inch.

Four bars 12, parallel to one another and to the shaft 4 and each having a series of teeth 13 on its outer surface, are sunk into slots 14 (Figure 3) so that the teeth 13 do not extend beyond the periphery of the screw conveyor 9.

A bafile 22, shown particularly in Figure 2, mounted within and rotated by the screw conveyor 9, extends diametrically across the drum 2 between two of the bars 12 and along the chamber 2 for the length of the bars 12.

In operation, alkali cellulose sheets which may have received a preliminary shredding in a pre-breaker l5, are fed through a hopper 16 into the feeding chamber 1. The screw conveyor 9, turning at about revolutions per minute, carries the alkali cellulose into the drum 2 where, by the action of centrifugal force, the alkali cellulose is thrown against the inner wall It) and is shredded between the teeth 11 and the teeth 13. The bafile 22 prevents alkali cellulose from passing through the drum 2 without being subjected to shredding between the teeth 11 and the teeth 13. The teeth 13 may be set at an angle such that they tend to move the alkali cellulose in opposition to the screw conveyor 9 or they may be set at right angles to the bars 12 or at any other desirable angle. The shredded alkali cellulose is carried forward into the collecting chamber 3 where it is flung off the end of the screw conveyor 9 towards the wall 20 of the chamber 3, falls under gravity and then passes out by way of a chute 1'] arranged at an angle such that no retention of crumbs occurs. The flow of the shredded alkali cellulose may be observed through a Window 18 in the chute 17.

Figure 4 shows an alternative form of collecting chamber 3. In this construction the wall 20' flares out from the wall of the drum 2 and alkali cellulose sweeps along the wall 20' before dropping into the chute 17, so reducing the tendency for particles to stick. In this embodiment the screw conveyor 9 stops short of the end wall 19 but it may extend to the end wall 19 if so desired.

In Figures and 6, the drum 2 has an end wall 23 and an outlet 24 in the wall 10. The screw conveyor 9 stops short of the end wall 23 but extends part Way over the outlet 24 so that shredded alkali cellulose passes freely through the outlet 24 into a chute 25 without packing against the end wall 23.

In apparatus according to the invention substantially all particles of the alkali cellulose are subjected to the same conditions throughout, which is desirable in making viscose because variations in the conditions to which particles are subjected can result in variations in the properties of the yarn spun from the viscose.

The drum 2 is in all cases surrounded by a jacket 21 through which a cooling or heating fluid may be circulated if desired. In addition, the baffle 22 may be hollow to carry cooling or heating fluids or other arrangements may be made for controlling the temperature within the apparatus.

What we claim is:

1. A drum shredder for alkali cellulose comprising a cylindrical drum having a shredding surface on its internal wall, a conveying rotor mounted centrally within said drum, having at least one cooperating shredding surface on its periphery and being capable of conveying alkali cellulose axially toward an outlet, driving means for rotating said rotor and thereby throwing alkali cellulose into an annular shredding region defined between the shredding surface of the drum and the coopcrating shredding surface of the rotor, in combination with an expansion chamber joined to said drum and having an outlet at its bottom, said shredding region merging into said chamber and said chamber having a diameter which increases from the point at which it joins the drum, said rotor protruding from said drum into said chamber directly above said outlet at the bottom of said chamber and said chamber being otherwise free from conveying structure whereby shredded alkali cellulose is freed from mechanical pressure prior to its discharge from the shredder.

2. A drum shredder for alkali cellulose comprising a cylindrical drum having a shredding surface on its internal Wall, a rotor capable of conveying alkali cellulose axially toward an outlet in the floor of said drum adjacent to a terminal wall thereof, said rotor being mounted centrally within said drum and comprising a shaft and a screw conveyor mounted on said shaft, said screw conveyor having slots in its peripheral edges, at least one bar mounted in said slots parallel to the axis of said conveyor, said bar having a series of teeth along its length and being so positioned in said slots that the teeth are in line with but do not extend beyond the periphery of said screw conveyor, said bar forming a shredding surface on the periphery of said conveyor, a baflle of width equal to the effective diameter of said screw conveyor dividing said conveyor longitudinally, and driving means for rotating said rotor so that the alkali cellulose is thrown into an annular shredding region defined between the shredding surface of said drum and the cooperating shredding surface of said conveyor, said shredding region merging into a chamber not swept by said rotor of diameter at least that of the interior of said drum, said rotor extending beyond said annular shredding region at the outlet end of said drum, said conveyor ending at a point midway over said outlet and said bar ending at a point directly above the edge of said outlet remote from the terminal wall of said drum so that the shredded alkali cellulose is freed from mechanical pressure prior to its discharge through said outlet.

References Cited in the file of this patent UNITED STATES PATENTS 1,046,678 Thiesing Dec. 10, 1912 1,447,834 Boswell Mar. 6, 1923 2,206,745 MacKenzie July 2, 1940 2,476,335 Tusson July 19, 1949 FOREIGN PATENTS 143,822 Germany Sept. 26, 1903 276,661 Switzerland Oct. 16, 1951 433,211 Italy Apr. 3, 1943 455,908 Germany Feb. 11, 1928 725,563 Germany Sept. 24, 1942 OTHER REFERENCES Chemical Engineering, August 1948, page 124. Photostat in Div. 55. 

1. A DRUM SHREDDER FOR ALKALI CELLULOSE COMPRISING A CYLINDRICAL DRUM HAVING A SHREDDING SURFACE ON ITS INTERNAL WALL, A CONVEYING ROTOR MOUNTED CENTRALLY WITHIN SAID DRUM, HAVING AT LEAST ONE COOPERATING SHREDDING SURFACE ON ITS PERIPHERY AND BEING CAPABLE OF CONVEYING ALKALI CELLULOSE AXIALLY TOWARD AN OUTLET, DRIVING MEANS FOR ROTATING SAID ROTOR AND THEREBY THROWING ALKALI CELLULOSE INTO AN ANNULAR SHREDDING REGION DEFINED BETWEEN THE SHREDDING SURFACE OF THE DRUM AND THE COOPERATING SHREDDING SURFACE OF THE ROTOR, IN COMBINATION WITH AN EXPANSION CHAMBER JOINED TO SAID DRUM AND HAVING AN OUTLET AT ITS BOTTOM, SAID SHREDDING REGION MERGING INTO SAID CHAMBER AND SAID CHAMBER HAVING A DIAMETER WHICH INCREASES FROM THE POINT AT WHICH IT JOINS THE DRUM, SAID ROTOR PROTRUDING FROM SAID DRUM INTO SAID CHAMBER DIRECTLY ABOVE SAID OUTLET AT THE BOTTOM OF SAID CHAMBER AND SAID CHAMBER BEING OTHERWISE FREE FROM CONVEYING STRUCTURE WHEREBY SHREDDED ALKALI CELLULOSE IS FREED FROM MECHANICAL PRESSURE PRIOR TO ITS DISCHARGE FROM THE SHREDDER. 